What Is the Purpose of a "Choice of Law" Clause

What is the purpose of a "choice of law" clause in an international contract?

A) to allow the plaintiff to choose which nation's law will be applied to a dispute
B) to allow the defendant to choose which nation's law will be applied to a dispute
C) to give the parties a chance to decide in which nation the lawsuit must be brought
D) to determine which nation's law will apply in settling disputes that arise under the contract
E) to determine whether a party must sue on the basis of law, or on the basis of equity